drm/atomic: Make add_affected_connectors look at crtc_state.

This kills another dereference of connector->state. connector_mask
holds all unchanged connectors at least and any changed connectors
are already in state anyway.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1484559464-27107-3-git-send-email-maarten.lankhorst@linux.intel.com